A polymer electrolyte fuel cell (PEFC) is a fuel cell in which a solid polymer electrolyte is interposed between an anode and a cathode, a fuel is supplied to the anode, oxygen or air is supplied to the cathode, whereby oxygen is reduced at the cathode to produce electricity. As the fuel, hydrogen, methanol or the like is mainly used. In order to increase a reaction rate of a fuel cell to thereby enhance energy conversion efficiency of the fuel cell, a layer containing a catalyst has been formed on a cathode surface or an anode surface of the fuel cell in the past. As this catalyst, a noble metal is generally used, and of noble metals, platinum that is stable at a high potential and has high activity is mainly used. As a carrier to support this catalyst metal, carbon black has been used in the past.
By the way, in this PEFC, the cathode is temporarily exposed to a high potential, e.g., about 1.5 V, during the repeating operations of starting and stopping. It is known that at such a high potential, carbon that is a carrier suffers oxidation corrosion to cause decomposition and deterioration of the carrier. Owing to deterioration of the carrier, power generation performance of the PEFC is lowered. Owing to deterioration of the carrier aggregation of the noble metal is accelerated, and therefore, the power generation performance is further lowered. Accordingly, a carrier or a catalyst having resistance to high potentials accompanying starting and stopping and a fuel cell electrode catalyst using it have been desired.
Patent literature 1 discloses a carrier for supporting a catalyst, which is obtained by carbonizing a raw material comprising a nitrogen-containing organic substance and a metal. Patent literature 2 discloses an electrode catalyst for a fuel cell, wherein the catalyst is produced by a production process comprising a step 1 of mixing a transition metal-containing compound, a nitrogen-containing organic compound and a solvent to obtain a catalyst precursor solution, a step 2 of removing the solvent from the catalyst precursor solution and a step 3 of heat-treating a solid residue at a temperature of 500 to 1100° C. to obtain an electrode catalyst, wherein a part or all of the transition metal-containing compound is a compound containing, as a transition metal element, a transition metal element M1 selected from elements of the periodic table Group 4 and Group 5. Patent literature 3 discloses a catalyst, which is a compound containing a metal element M selected from the group consisting of titanium, iron, niobium, zirconium and tantalum and shows peaks at 1340 cm−1 to 1365 cm−1 and 1580 cm−1 to 1610 cm−1 when measured by Raman spectroscopy. Patent literature 4 discloses a catalyst carrier comprising a metal oxycarbonitride containing niobium or the like as a metal. Patent literature 5 discloses an electrode catalyst produced by subjecting a carbon material having a noble metal supported thereon to heat treatment. Patent literature 6 discloses that acetylene black having a high specific surface area is obtained by subjecting acetylene black to oxidation treatment, and also discloses a catalyst for a fuel cell, wherein the catalyst comprises this acetylene black and, supported thereon, a platinum particle or the like.
However, any of the above carriers and catalysts does not have sufficient resistance to high potentials accompanying starting and stopping.